1. Field of Invention
The invention is directed to semi-conductor wafer preparation and fabrication, and more particularly, to a single machine which may be utilized in performing multiple preparation and fabrication techniques on a wafer, including chemical mechanical polishing, wet chemical treatment and oxidation.
2. Description of the Prior Art
Machines for preparing and fabricating semi-conductor wafers are known in the art. Wafer preparation includes slicing semi-conductor crystals into thin sheets, and polishing the sliced wafers to free them of surface irregularities, that is, to achieve a planar surface. In general, the polishing process is accomplished in at least two steps. The first step is rough polishing or abrasion. This step may be performed by an abrasive slurry lapping process in which a wafer mounted on a rotating carrier is brought into contact with a rotating polishing pad upon which is sprayed a slurry of insoluble abrasive particles suspended in a liquid. Material is removed from the wafer by the mechanical buffing action of the slurry. The second step is fine polishing. The fine polishing step is performed in a similar manner to the abrasion step, however, a slurry containing less abrasive particles is used. Alternatively, a polishing pad made of a less abrasive material may be used. The fine polishing step often includes a chemical mechanical polishing ("CMP") process. CMP is the combination of mechanical and chemical abrasion, and may be performed with an acidic or basic slurry. Material is removed from the wafer due to both the mechanical buffing and the action of the acid or base.
In wafer fabrication, devices such as integrated circuits or chips are imprinted on the prepared wafer. Each chip carries multiple thin layers of conducting metals, semiconductors and insulating materials. Layering may be accomplished by growing or by deposition. For example, an oxide layer may be grown on the surface of the chip to serve as an insulating layer. Alternatively, a metal layer may be anodized in a fluid bath to create an insulating oxide layer. Common deposition techniques include chemical vapor deposition, evaporation and sputtering, which are useful in applying layers of conductors and semiconductors. After a layer is applied, it is further processed in a series of patterning steps, in which portions of the added layer are removed. Patterning may be accomplished by techniques such as etching. Doping and heat treatment steps also are necessary during chip fabrication. A plurality of layers are applied, patterned, doped and heat treated during fabrication to create the finished chip. The individual layers also are polished and cleaned during fabrication.
In general, the currently available technology for chip fabrication requires that each step be performed on a separate machine. The use of separate machines wastes the limited space available in fabrication facilities. Further, it is not uncommon for chips to have as many as ten separate layers which must be separately applied, polished and processed. Accordingly, the necessity for moving chips between machines for each production step compromises efficiency, and increases the risk of the wafers being damaged or contaminated.
A device for performing multiple process steps on semi-conductor wafers is disclosed in U.S. Pat. No. 4,481,741 to Bouladon et al, incorporated by reference. The machine disclosed in Bouladon includes a rotating plate which includes a wheel and a solid disc which is disposed on the upper surface of the wheel. A collar is disposed in a groove which divides the disc into inner and outer zones. The inner zone is covered by a first substrate or polishing pad and the outer zone is covered by a second substrate or polishing pad having a different nature. That is, one substrate may be harder or more abrasive than the other.
The Bouladon machine may be used to perform a two-phase polishing procedure on a cut wafer. In the first phase, rough polishing is performed by rotating the plate, and simultaneously spraying an abrasive slurry on the outer substrate while lowering the spinning wafer into contact with the substrate to perform abrasive or rough polishing. After completion of abrasive or rough polishing, the wafer is raised and pivoted by movement of an arm into a position over the inner substrate, which also is sprayed with a polishing slurry. The spinning wafer is lowered into contact with the inner substrate to perform fine polishing.
The Bouladon machine is directed primarily to initial wafer preparation, that is, smoothing and planarizing the wafer surface in preparation for further chip fabrication. Accordingly, Bouladon is directed to performing different aspects of the same process, that is, wafer polishing, and does not disclose the performance of two distinct processes on the same machine. Bouladon has no provision for performing non-polishing steps such as oxidation, anodization, etching or cleaning, each of which is essential in chip fabrication. Further, Bouladon also does not disclose the use of CMP processes, which have become essential in current chip fabrication techniques. Accordingly, the use of the Bouladon machine in chip fabrication would be limited.